Managing Wastes in Aquaculture

Aquaculture has been widely practiced in China and other Asian countries and the history goes back over 2000 years. Commercial aquaculture is conducted in earthen ponds and the quality of the water used has to be constantly monitored for the health of the marine life.

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Aquaculture Produces Affluent

Aquaculture is quite often classified with agricultural activities and standards for effluent from such fish farms are judged accordingly. Thirty percent of the feed used in aquaculture tends to become waste. This is in addition to the other waste produced by the fish excreta. All this waste reduces the oxygen content in the water and can affect marine life. It is therefore very necessary to constantly monitor the condition of the water and remove it for re-treatment before reuse.

Aquaculture or fish farming can produce effluents that can have an adverse effect on the rivers and watercourses that such effluent may be drained into. Water itself is a very scarce resource and it therefore makes sense to treat the effluent from aquaculture and reuse the water. Quite often this can also make a lot of sound economic sense. Land-based aquaculture and fish farms produce effluents in the form of water and solids. The water will have dissolved nutrients and other substances. Solids come from inorganic sources like sand or soil from the floor of the fish ponds and organic substances in the form of algae, uneaten food, and others.

The Need to Treat Aquaculture Affluent

Aquaculture effluent reuse involves the treatment of such wastewater containing dissolved substances and other solid waste. As aquaculture is normally carried out in vast open lands, the possibility of such wastewater affecting surrounding groundwater sources has also to be given equal attention. The quality of water used to farm fish also has an effect on their growth and health. This requires the constant replenishment of the water and treating and reusing the water can drastically reduce costs. Ammonia is the principal nitrogenous waste produced by fishes and high concentrations of this can lead to tissue damage and reproductive damage. Aquaculture effluent reuse allows reduction of water input and allows control of the environment that encourages the growth of fish.

The Treatment of Affluent

Aquaculture effluent can be treated and the water reused by the adoption of bio-filters and other means. The treatment of the effluent water involves the use of mechanical and biological filtration. Mechanical filtration will involve the removal of particulate waste while the dissolved wastes are removed through biological reactions. Such solid waste can also be removed by settling tanks but this would mean land use to build such tanks. A number of aquaculture farms use wind power to produce the power needed for the operation of such mechanical filtration systems. These systems involve the screening of the waste water through small sized mesh with the use of pumps and containers which contain the screens. The effluent free from the solid waste is then sent forward for bio-filtration.

Several types of bio-filters are in use and each of them has their own different operational characteristics. The most common among these is a rotating biological contactor with a trickling filter and a bead bed filter. A bio-film in the drum that is rotating allows the alternate submerging of the film so that it constantly gains oxygen needed for the process of filtration. The waste water is then led through the trickle down filter which has filter medium inside it. The final process is through the bead filter which is a bed of small plastic beads that have density lower than that of water. It is necessary to constantly clean these filters for maintaining the efficiency of the filters.

Reverse Osmosis is also a process used for cleaning of aquaculture affluent. However, this is a power hungry solution and needs this to be evaluated before it is adopted as a cleaning solution. The efficiency of such membranes is very high. Studies have also been made about using wastewater from aquaculture as a starting point for aquaponics or the growing of vegetative growth from this water after removing the solid waste by sedimentation. Where sedimentation is used to treat aquaculture affluent, a means to use this sediment as fertilizer or other means must be examined.